1. Field of the Invention
This invention relates to the discovery of the optimum singular soft organic material, and its particle-size range concentration, combined with a suitable clay or polymer viscosifier, which will completely seal seepage loss of workover or completion fluids in permeable, pressure depleted formations. This invention will replace the need for sized limestone, calcium carbonate, or salt and their inherent disadvantages. This new processed material will also eliminate the usual need for a fluid loss control agent, such as starch, mica, etc.
Workover and completion fluids are used to rework a drilled well, or to complete an oil, gas, or mineral recovery well after it has been drilled. The fluid which was used to drill the well is sometimes used to complete the well; however, this fluid frequently interferes with either the completion operations, or production of the well when these procedures are finished. Therefore, workover and completion fluids, non-damaging to the formation are needed.
2. Description of the Prior Art
In U.S. Pat. No. 3,198,268, Aug. 3, 1965, Lindblom, et al, disclosed the development of fermentates produced in carbohydrate solutions of the bacteria of genus Xanthomonas. The resulting product, Xanthan gum, had characteristics similar to bentonite clay slurries used to drill oil and gas wells, but did not have the detrimental effects to completion operations as the clay slurries.
However good Xanthan gum is as a viscosifier, it lacks fluid loss control needed for a completely non-damaging fluid. Typical fluid loss or seepage control agents, such as starch, mica, hard nut shells, etc., are too permanent, and interfere with production of the well after completion.
The use of finely divided calcium carbonate (limestone) as a fluid loss agent, combined with viscous fluids such as hydroxyethylcellulose or polyoxyethylene was described by Barkman, et al, in U.S. Pat. No. 3,516,496, Jun. 23, 1970. Barkman, et al, also discovered that guar gum damaged formations, and was not recommended as a viscosifier.
The disadvantage of calcium carbonate as a fluid loss sealing agent is that it must be dissolved with acid before the well can be brought into production. Mondshine in U.S. Pat. Nos. 4,175,042, 4,186,803, and 4,369,843, discloses the use of high concentrations of sized salt as a sealing agent, when combined with the various viscosifiers previously described. His procedures require that the salt solution be super-saturated, so that the sized salt will not dissolve, and thus lose its sealing effect. This is difficult to achieve in practice because deep wells are much hotter at bottom hole than on the surface, so the salt tends to dissolve as it is pumped down hole. The process of removal requires that a non-saturated water solution be used to wash the salt away, when other completion or workover operations are finished. This can be dangerous as the non-saturated water is lighter than the super-saturated fluid used to complete the well, and a "kick" may occur.